Re: [PATCH v4 2/2] rtc: max31335: add driver support

[Guenter Roeck]

On 11/2/23 09:57, Alexandre Belloni wrote:
[ ... ]
> > > > +static int max31335_read_offset(struct device *dev, long *offset)
> > > > +{
> > > > +	struct max31335_data *max31335 = dev_get_drvdata(dev);
> > > > +	u32 value;
> > > > +	int ret;
> > > > +
> > > > +	ret = regmap_read(max31335->regmap, MAX31335_AGING_OFFSET,
> > > &value);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	*offset = value;
> > >
> > > This is super dubious, what is the unit of MAX31335_AGING_OFFSET ?
> >
> > There is not additional information on the AGING_OFFSET register (no
> > other offset registers).
> > I treated it as a raw value that user can write/read. Should I drop the
> > offset implementation?
>
> The value exposed to userspace is in parts per billion. If you can't do
> the conversion, then you have to drop it.

The max31334 datasheet says "Resolution = 0.477ppm". Again, the datasheet for
max31335 is not public, so it is impossible to say what the resolution is
for that chip, but I would assume that it is documented.

Guenter